This invention relates to panel structures and to plastic pallets embodying panel structures according to the invention.
Panel structures are in wide use for construction purposes and fabricating purposes. Prior art panel structures have been formed of either metal, a paper product such as cardboard, wood, or synthetic materials such as plastic. Panel structures ideally are lightweight, strong, durable and maintenance-free, provide all-weather performance, and are relatively inexpensive. Whereas a plurality of metal, paper, wood, and plastic panel structures have been proposed over the years, none have totally satisfied all of the above-noted criteria.
Panel structures are also widely used in packaging and, specifically, in the formation of pallets. Pallets have traditionally been formed of wood. Wood pallets, however, have many disadvantages. For example, they are subject to breakage and thus are not reusable over extended periods of time. Wood pallets also take up a considerable amount of valuable floor space in the warehouse when they are not in use. In an effort to solve some of the problems associated with wood pallets, plastic pallets have been developed and employed with some degree of success. In one generally successful form of plastic pallet design, upper and lower plastic sheets are formed in separate molding operations and the two sheets are then selectively fused or knitted together in a suitable press to form a reinforced double wall or "twin sheet" structure. These twin sheet plastic pallets, although substantially more durable than the wooden pallets that they replace, tend to have a substantially higher initial cost than the corresponding wooden pallets due in large part to the relatively high cost of the raw plastic material required to form the pallet. It is therefore critical that the twin sheet type of pallet embody a structural design that maximizes the structural strength of the pallet for a given amount of plastic material employed to form the pallet. One form of twin sheet type plastic pallet that provides high structural strength for a given amount of plastic material is shown in applicant's U.S. Pat. No. 4,879,956. However, even the improved design of this patent is unable to provide the necessary rigidity required for many pallet applications without utilizing increased amounts of plastic material and thereby adding to the expense of the pallet.